This invention relates to a method of and an apparatus for dressing the cutting edge of a cut-off wheel which is used, for example, for cutting an ingot of semiconductor material into semiconductor wafers.
In the cutting of a block of semiconductor material such as a silicon ingot into slices to produce semiconductor wafers, a cut-off wheel having an inner peripheral cutting edge is generally utilized. As shown in FIG. 1, this cut-off wheel W is of a disc-like configuration and has an aperture 1 formed at the center thereof. An inner peripheral cutting edge 2 which comprises an electrically deposited diamond-grain coating and the like, is formed along the entire inner peripheral portion of the wheel W. The cut-off wheel W is secured to a rotary cutting machine by means of attaching holes 3 circumferentially disposed in the outer peripheral portion of the wheel W and is rotated at a high speed by the cutting machine to cause the inner peripheral cutting edge 2 to cut, into slices, a silicon ingot 4 which is inserted into the aperture 1 and moved in a direction parallel to the cut-off wheel W, as indicated by arrow A.
The sharpness of such cut-off wheel decreases as the cutting operation is repeated since the cutting edge 2 is worn down and the pores on the surface of the cutting edge 2 become clogged with a powdery substance. This decrease in sharpness causes a variation in thickness and a warp or curvature of the cut slices of the ingot, which results in a deterioration in quality of the semiconductor wafers. For this reason, it is necessary for the cut-off wheel to be occasionally applied with a dressing treatment to remove the powdery substance from the pores and to resharpen the cutting edge.
Conventional dressing treatment is applied to the cut-off wheel, for example, according to the manner of manual dressing. In the manual dressing, an abrasive stick 5, as shown in FIG. 2, is brought into slight contact with a dulled portion of the cutting edge 2 of a rotating cut-off wheel W and is slid in a direction indicated by arrow B to dress the cutting edge 2 gradually. However, a great skill is required for continuously effective dressing, since it is difficult for the abrasive stick to maintain a proper state of contact with the cutting edge 2 and since inadequate pressing of the abrasive stick against the cutting edge causes, on the cutting edge 2, such damage that the diamond grains fall off.
U.S. Pat. No. 4,699,118 discloses a dressing apparatus for automatically applying a dressing to the cutting edges of cut-off wheels. As shown in FIG. 3, this apparatus utilizes two abrasive tapes 6 and 7 travelling across a cut-out 8 which is formed in the head portion 9 of the apparatus. In the cut-out 8, the abrasive tapes 6 and 7 extend in directions crossing each other so that tapes 6 and 7 are able to contact respectively the opposite side surfaces 10 and 11 of the cutting edge 2 of a cut-off wheel W. However, the head portion 9 is movable merely in a direction parallel to the cut-off wheel W, and thus it is not easy for the head portion to bring the alternative of the two tapes 6 and 7 into contact with the cutting edge 2.